Problem: $-\dfrac{5}{12} + \dfrac{1}{8} = {?}$
Answer: $ = - {\dfrac{5 \times 2}{12 \times 2}} + {\dfrac{1 \times 3}{8 \times 3}} $ $ = - {\dfrac{10}{24}} + {\dfrac{3}{24}} $ $ = - \dfrac{{10} + {3}}{24} $ $ = -\dfrac{7}{24}$